[DataLoader] Adding demux and mux DataPipe-s (#61234)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61234
* **#61234 [WIP] Adding demux and mux DataPipe API examples**
Test Plan: Imported from OSS
Reviewed By: ejguan
Differential Revision: D29588836
Pulled By: VitalyFedyunin
fbshipit-source-id: 523d12ea6be7507d706b4c6d8827ec1ac4ccabc3
